Rotary Motor Driven Reciprocating Downhole Pump Assembly

ABSTRACT

A motor and pump assembly for use in a wellbore includes a downhole motor producing a rotary output, a reciprocating plunger for pumping fluid up a tubing string, and a drive linkage supported within the hollow tubular housing having a rotary input in connection with the rotary output of the motor and a reciprocating output which is arranged for longitudinal sliding movement with the reciprocating plunger and which is driven responsive to rotation of the rotary input to drive the plunger. The drive linkage includes a lead screw, a sleeve member having a closed end coupled to the plunger, and a follower supported on an inner side of the sleeve member in operative connection to the lead screw to drive longitudinal sliding movement of the sleeve member responsive to rotation of the lead screw.

This application claims the benefit under 35 U.S.C.119(e) of U.S. provisional application Ser. No. 62/330,352, filed May 2, 2016.

FIELD OF THE INVENTION

The present invention relates to a drive assembly including a rotary motor for connection to a reciprocating pump assembly for use in a wellbore with a production tubing string having a production passage therein and at least one pump control line alongside the production tubing string.

BACKGROUND

In the production of hydrocarbon fluids from a wellbore, it is common to employ artificial lift in instances where the downhole pressure is insufficient to lift the produced fluids to the wellhead.

One form of artificial lift comprises a progressive cavity pump in which a rotor is rotated within a stator such that cavities between the rotor and the surrounding stator progress upwardly as the rotor is rotated for lifting fluids. Progressive cavity pumps however have a limited depth of operation. Furthermore, a typical progressive cavity pump is driven by a rotating rod string which can produce wear in the surrounding casing, particularly when used in wells having a horizontal section.

Another form of artificial lift comprises use of a jet pump to accelerate fluid flow to carry the produced fluids upward, however, use of a jet pump can be limited in depth as well.

Reciprocating pumps are known to be used to provide sufficient lift for deeper wells, however, driving of a reciprocating pump typically requires a rod string extending between the downhole pump and the surface, resulting in wear problems between the rod string and the surrounding casing, particularly when there are horizontal sections in the wellbore.

In deeper horizontal well types, there are presently two forms of artificial lift that are generally used. The first is gas lift, which can be installed at any deviation, however, it is expensive and very inefficient as deviations increase from a few degrees past vertical. Also this fluid lift type will become inoperative as well reservoir pressure decreases below the gas injection pressure needed to lift the hydrostatic column of fluid from the well. The second form of lift, beam lift, is required to be landed in the vertical section of the well to avoid mechanical wear as the rods stroke inside the production tubing. The consequence to landing the bottom hole pump in the vertical section is the loss of productivity due to leaving a column of fluid in the horizontal build section above the horizontal lateral.

Chinese patent application CN 2165260 discloses an example of a linear reciprocating pump which is driven to reciprocate linearly by a rotary-to-linear conversion linkage supported downhole adjacent to the reciprocating pump. A rod string is thus required to communicate between the wellhead and the linkage to provide an input rotation, however, the rod string causes wear problems relative to the surrounding casing, particularly when the wellbore includes horizontal sections. Furthermore produced fluids are required to be directed upwardly through the casing surrounding the conversion linkage so that the driving screw can become plugged with sand and other debris from the produced fluids which can prevent proper operation of the linkage. This results in costly maintenance and loss of productivity.

U.S. Pat. No. 1,842,457 by Mendenhall et al discloses a submersible motor and reciprocating pump which also provides a conversion linkage downhole for operation between a rotary input and the reciprocating pump to convert the rotary input into a reciprocating linear output that drives the reciprocating pump. The linkage is not well suited for conversion of the high forces needed for lifting from deeper wells. The input rotation is provided by a submersible electric motor mounted downhole below the reciprocating pump. The configuration of the motor necessitates that the production string communicate with the surrounding wellbore at the base of the reciprocating pump which corresponds to a location along the string which is spaced upwardly considerably from the motor at the bottom end. Locating the fluid intake at a location spaced well above the bottom end of the string can result in considerable sand deposits and the like collecting about the motor, making it difficult to retrieve the motor, and/or to relocate the production string.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a motor and pump assembly for use in a wellbore with a production tubing string having a production passage therein and at least one pump control line alongside the production tubing string, the pump assembly comprising:

a motor housing portion comprising:

-   -   a hollow tubular housing arranged to be supported at a bottom         end of the production tubing string;     -   a motor supported within the hollow tubular housing for         connection to said at least one pump control line for driving         rotation of a rotary output of the motor;     -   a drive linkage supported within the hollow tubular housing         having a rotary input in connection with the rotary output of         the motor and a reciprocating output which is arranged for         longitudinal sliding movement relative to the hollow tubular         housing responsive to rotation of the rotary input; and     -   an auxiliary conduit extending externally alongside the hollow         tubular housing and having a production passage therein for         connection in series with the production passage of the         production tubing string;

a plunger housing portion comprising;

-   -   a hollow tubular housing arranged to be supported at the bottom         end of the production tubing string in series with the hollow         tubular housing portion of the motor housing portion, the hollow         tubular housing portion of the plunger housing portion having a         production passage therein for connection in series with the         production passages of the auxiliary conduit and the production         tubing string;     -   a stationary check valve supported at a stationary location         within the hollow tubular housing of the plunger housing portion         to span across the production passage therein so as to be         operable to only allow an upward flow of production fluid         therethrough;     -   a plunger supported within the production passage of the plunger         housing portion so as to be longitudinally slidable relative to         stationary check valve;     -   a movable check valve supported on the plunger for longitudinal         sliding movement together with the plunger relative to the         plunger housing portion, the movable check valve being operable         to only allow an upward flow of production fluid therethrough.

The drive linkage may comprise: (i) a lead screw which is rotatable with the rotary input at a stationary position in the longitudinal direction relative to the motor housing portion; (ii) a sleeve member supported within the hollow tubular housing of the motor housing portion for longitudinal sliding movement, the sleeve member having a hollow interior extending longitudinally between an open end receiving the lead screw therein and a closed end coupled to the plunger; and (iii) a follower supported on an inner side of the sleeve member in operative connection to the lead screw to drive longitudinal sliding movement of the sleeve member responsive to rotation of the lead screw.

The follower may comprise a plurality of planetary screws rotatably supported on the sleeve member at circumferentially spaced apart locations about the lead screw.

An annular sealing member may be in operative connection between the sleeve member and the housing tubular housing of the motor housing portion so as to isolate the lead screw from the production passage of the plunger housing portion. Hydraulic oil is preferably contained in a closed chamber surrounding the lead screw.

An end sub may be supported at a bottom end of the production tubing string in which the end sub has a plurality of inlet openings at a bottom end of the end sub such that the production passages of the plunger housing portion and the auxiliary conduit are connected in series between the production passage of the production tubing string thereabove and the inlet openings of the end sub therebelow.

The motor housing portion may be supported below the plunger housing portion. In this instance, said at least one pump control line preferably extends externally alongside the plunger housing portion.

Alternatively, the motor housing portion may be supported above the plunger housing portion such that the production passage of the auxiliary conduit communicates in series between the production passage of the plunger housing portion therebelow and the production passage of the tubing string thereabove.

When the motor comprises a hydraulic motor, said at least one pump control line preferably comprises a first hydraulic line and a second hydraulic line connected in a loop between the motor and a hydraulic supply at a wellhead of the wellbore for driving the motor. In this instance, a hydraulic switching motor may be arranged to periodically reverse flow in the first and second hydraulic lines so as to periodically reverse rotation of the rotary input and corresponding longitudinal movement of the reciprocating output of the drive linkage.

Alternatively, the motor may comprise an electric submersible motor and said at least one pump control line comprises an electric circuit in communication between the electric submersible motor and a power source at a wellhead of the wellbore for driving the motor.

According to a second aspect of the present invention there is provided a drive assembly for use in a wellbore with a production tubing string supporting a reciprocating pump assembly at a bottom end thereof, and including at least one pump control line alongside the production tubing string, the drive assembly comprising:

a hollow tubular housing arranged to be supported at a bottom end of the production tubing string in series with the reciprocating pump assembly;

a motor supported within the hollow tubular housing for connection to said at least one pump control line for driving rotation of a rotary output of the motor; and

a drive linkage supported within the hollow tubular housing having a rotary input in connection with the rotary output of the motor and a reciprocating output which is arranged for connection to the reciprocating pump assembly;

the drive linkage comprising:

-   -   a lead screw which is rotatable with the rotary input at a         stationary position in the longitudinal direction relative to         the motor housing portion;     -   a sleeve member supported within the hollow tubular housing for         longitudinal sliding movement, the sleeve member having a hollow         interior extending longitudinally between an open end receiving         the lead screw therein and a closed end including a coupling for         connection to the reciprocating motor; and     -   a follower supported on an inner side of the sleeve member in         operative connection to the lead screw to drive longitudinal         sliding movement of the sleeve member responsive to rotation of         the lead screw.

The follower may comprise a plurality of planetary screws rotatably supported on the sleeve member at circumferentially spaced apart locations about the lead screw.

The drive assembly may also include an annular sealing member in operative connection between the sleeve member and the housing tubular housing so as to isolate the lead screw from production fluids within a production passage of the reciprocating pump assembly.

Preferably hydraulic oil is contained in a closed chamber surrounding the lead screw.

Use of a rotary motor together with a linkage to drive a linear reciprocating pump provides a pump assembly which provides high lift for use in deep wells, without concern for rod string wear.

The addition of an auxiliary conduit alongside the motor housing ensures that the production fluid intake can be located at the bottom end of the string even when using a rotary motor for driving a linear pump.

Furthermore, the configuration of the drive linkage including a sleeve member which reciprocates relative to a lead screw received therein provides an improved linkage which can transfer high amounts of force from a rotary input to a linear output, while remaining isolated from the wellbore fluids by the surrounding sleeve to overcome the deficiencies of the prior art.

Some embodiments of the invention will now be described in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a first embodiment of the motor and pump assembly connected to the bottom end of a production tubing string within a wellbore;

FIG. 2 is an enlarged schematic view of the drive linkage between the motor and the reciprocating pump assembly according to the first embodiment of FIG. 1;

FIG. 3 is a schematic view of a second embodiment of the motor and pump assembly; and

FIG. 4 is a schematic view of a further embodiment of the motor and pump assembly.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

Referring to the accompanying figures there is illustrated a production string generally indicated by reference numeral 10. The production string is intended for use within a wellbore 12 for producing hydrocarbon fluids from the well using artificial lift.

According to the illustrated embodiment, the production string uses a multi-conduit coiled tubing member 14 deployed with a coiled tubing injector. The coiled tubing member includes a production tubing conduit 16 defining a production passage therein which extends longitudinally between the wellhead and a downhole motor and pump assembly 18 described in further detail below. Produced fluids from the wellbore are directed up the production passage for communication to a production storage tank at the surface in proximity to the wellhead. The coiled tubing member 14 further includes two pump control lines 20 which extend alongside the production conduit. Each pump control line 20 comprises a hydraulic conduit for conveying hydraulic fluid therethrough between the wellhead and the downhole motor and pump assembly 18 at the bottom end of the production string.

Although various embodiments of the motor and pump assembly 18 are contemplated herein, the common features of the various embodiments will first be described.

The motor and pump assembly 18 includes a motor housing portion 22 and a plunger housing portion 24. The housing portions each comprise a hollow tubular housing member, in which the housing members are connected longitudinally in series with one another, either as a single, integral, continuous casing, or as a pair of separate casings which are jointed to one another by conventional means.

The hollow interior of the plunger housing portion 24 defines a production passage therein which communicates longitudinally between opposing open ends of the plunger housing portion.

The motor housing portion 22 supports an auxiliary conduit 26 extending parallel to and alongside the tubing member of the motor housing portion, externally of the tubing member, so as to define a production passage extending longitudinally therethrough.

An end sub 28 is connected to the bottom end of the string and includes a hollow interior defining a production passage communicating longitudinally therethrough from a plurality of inlet openings 30 at the bottom end of the end sub to a top end of the end sub.

The motor housing portion 22 and the plunger housing portion 24 are connected in series with one another between the bottom end of the multi-conduit coiled tubing member 14 thereabove and the end sub 28 therebelow such that the production passage of the auxiliary conduit 26 and the production passage of the plunger housing portion 24 are connected in series communication between the production passage of the end sub 28 therebelow and the production passage of the production tubing conduit 16 thereabove. In this manner produced fluids enter through the inlet openings 30 at the bottom end of the assembled production string 10 for communication upwardly through the production passages to the wellhead.

The motor housing portion 22 has a hollow interior communicating between an open end 32 which is an open communication with the plunger housing portion 24 coupled thereto, and an opposing closed end 34. A hydraulic motor 36 is mounted within the hollow interior of the motor housing portion 22 adjacent the closed and 34. Suitable passages communicate from the motor 36 through the motor housing portion to an exterior for connection to the two pump control lines 20 respectively. The two pump control lines are operated as a hydraulic circuit to provide a hydraulic supply and hydraulic return operating between the motor 36 and a suitable hydraulic supply 90 at the wellhead.

A rotary output of the motor 36 is coupled to a rotary output member 38 which is rotatably supported relative to the tubular housing of the motor housing portion 22 so as to be coaxial with a longitudinal axis of the motor housing portion. Annular sealing members 40 are provided about the output shaft of the motor, between the motor and the rotary output member. An annular bearing 42 is coupled between an inner surface of the motor housing portion 22 and the rotary output member 38 to support the rotary output member for rotation relative to the tubular housing. The seals about the output of the motor provide a seal at one end of an oil chamber 44 described in further detail below.

A shaft coupling 46 on the rotary output member supports a lead screw 48 thereon which extends longitudinally relative to the motor housing portion for rotation coaxially with the rotary output member relative to the surrounding tubular housing. The lead screw 48 is part of a drive linkage within the motor housing portion which converts an input rotation from the rotary hydraulic motor 36 to a linear output motion for driving a reciprocating plunger 50 within the plunger housing portion 24 as described in further detail below.

A sleeve member 52 is located within the motor housing portion for being received coaxially about the lead screw 48. The sleeve member 52 has a suitable diameter for being received coaxially between the lead screw and the surrounding tubular housing of the motor housing portion. The sleeve 52 spans the full length of the lead screw such that the lead screw and sleeve member each define a stroke length of the reciprocating plunger 50 within the plunger housing portion 24.

The sleeve member 52 is a tubular member extending between an open inner end 54 receiving the lead screw therethrough for connection to the rotary output member 38 of the motor, and an opposing closed outer end 56 which provides a sucker rod connection 58 thereon for connection to the plunger 50. The sleeve member is constrained relative to the surrounding motor housing portion, for example by a keyed connection, such that the sleeve member is linearly slidable relative to the surrounding housing while relative rotation between the sleeve and the surrounding housing is prevented.

At the inner end 54 of the sleeve 52, a plurality of planetary screws 60 are mounted at the inner side of the sleeve at circumferentially spaced positions about the lead screw, in threaded connection with external threads of the lead screw. The planetary screws 60 are supported rotatably on the sleeve member for rotation about respective longitudinally oriented axes, while remaining fixed in position relative to the sleeve member. In this arrangement as the lead screw is rotated, the planetary screws 60 are similarly rotated relative to their respective longitudinal axes, but in a manner which causes the sleeve member to be longitudinally displaced between opposing first and second positions. In the first position, the lead screw is fully received within the sleeve such that the inner end of the sleeve is in close proximity to the rotary output member of the motor. In the second position the sleeve member protrudes into the plunger housing portion such that the inner end of the sleeve member 52 is located in proximity to the outer end of the lead screw. A seal sub 62 is provided in the form of an annular sealing member mounted within the annular gap between the sleeve member 52 and the surrounding tubular housing of the motor housing portion. The seal sub allows relative longitudinal sliding between the sleeve member and the surrounding housing while providing a sealing interface between the sliding sleeve member and the housing. The seal sub 62 provides a seal at the opposing end of the oil chamber 44 which is defined between the seal 40 of the rotary output member and the seal of the seal sub 62. This enables hydraulic oil to occupy the oil chamber 44 surrounding the lead screw to maintain lubrication between the lead screw and the planetary screws 60 which function as followers in operative connection with the lead screw 48. The seal sub 62 is supported at the interface between the motor housing portion 22 and the plunger housing portion 24.

The plunger 50 has a body which fully occupies the cross sectional area of the hollow interior of the plunger housing portion 24. The plunger body 50 thus assists in defining an inner chamber 63 between i) sealing engagement of the seal sub 62 with the sleeve member 52 at one end and ii) the plunger body 50 at the longitudinally opposing end of the chamber. The inner chamber 63 communicates with one end of the auxiliary conduit 26 throughout reciprocating movement of the plunger and sleeve member relative to the tubular housing.

An annular groove is provided about the outer circumference of the plunger body for locating an annular sealing member 64 therein which maintains a sealed contact between the plunger body and the surrounding tubular housing of the plunger housing portion 24. The sealing member 64 is retained within the annular groove in the plunger body for sliding movement together with the plunger body relative to the plunger housing portion 24.

The plunger 50 includes a central port 66 extending in the direction the longitudinal axis therethrough. An inner end of the central port 66 communicates with a plurality of circumferentially spaced radial ports 68 which communicate with the inner chamber 63 at circumferentially spaced positions about the rod connection 58.

The opposing outer end of the central port defines a seat 70 for receiving the ball 72 of a movable check valve 74. The ball sits above the seat to close the central port 68 through the plunger body when the plunger is displaced upwardly due to the weight of fluid pushing downwardly onto the ball, however, when the plunger is displaced downwardly, fluid pressure in the inner chamber relative to the fluid pressure above the plunger causes the ball 72 to lift from the seat, thus opening the central port 66 for communication with the space above the check valve. A ball cage 76 surrounds the ball and maintains the ball in close proximity to the seat even when in the open position to readily align the ball to close upon the seat when the plunger returns to an upward motion.

The plunger housing portion also locates a stationary check valve 78 therein which comprises a valve seat 80 mounted at a fixed location within the interior of the plunger housing portion, in sealed engagement with the inner surface thereof. A ball 82 sits upon the seat 80 to close the check valve and prevent fluid flow across the check valve when the plunger is displaced downwardly relative to the stationary check valve 78. When the plunger is displaced upwardly, the fluid pressure below the stationary check valve exceeds the fluid pressure above the stationary check valve such that the ball is lifted from the seat to open the valve. A suitable ball cage 84 is similarly provided about the ball of the stationary check valve to maintain the ball in close proximity to the valve seat even in the open position. Both ball cages include radial ports therein to allow fluid to readily pass through the ball cage when the check valve is open.

The movable and stationary check valves effectively define a pumping chamber 86 therebetween which fills with fluid when the movable check valve is displaced in one direction, and advances the charger fluid in the pumping chamber to a location above the valves when the movable check valve is stroked in the opposing direction.

The connection of the auxiliary conduit 26 alongside the motor housing such that it communicates through the walls of the housing from a location below the motor housing to a location above the motor housing enables a continuous production passage to be defined from the end sub, through the plunger housing portion, and through the auxiliary conduit, up to the production conduit of the coiled tubing member to ensure a continuous flow of produced fluids upwardly through the production string as the plunger is reciprocated, while the drive linkage remains isolated from produced fluids within the motor housing portion 22. A check valve 88 is connected in series with the auxiliary conduit 26 at the end of the conduit nearest to the plunger housing portion 24. The check valve 88 is configured to only allow upward flow through the production passage in the auxiliary conduit.

To provide an alternating rotary input, the motor and pump assembly is used together with the hydraulic supply 90 above ground at the wellhead of the wellbore which communicates with the two hydraulic pump control lines 20. A switching valve 92 is connected in series between the hydraulic supply 90 and the two pump control lines at the wellhead. The switching valve is reciprocated between first and second positions. In the first position, hydraulic fluid is supplied through a first one of the pump control lines to drive rotation of the motor 36 in a first direction and hydraulic fluid is returned through a second one of the pump control lines. In the second position, hydraulic fluid is supplied through the second pump control line to drive rotation of the motor 36 in a second direction opposite to the first direction and hydraulic fluid is returned through the first one of the pump control lines. Timing of the reciprocation between first and second positions of the switching valve 92 is arranged to drive rotation of the rotary motor in each direction a sufficient duration to accomplish a complete longitudinal stroke of the sleeve along the lead screw in one respective direction of linear movement.

Turning now to the preferred embodiment of FIGS. 1 and 2, in this instance the motor housing portion 22 is provided below the plunger housing portion. Accordingly the auxiliary conduit 26 in this instance communicates between the end sub 28 at the bottom end thereof below the motor and the plunger housing portion at the top end thereof above the motor. The top end of the auxiliary conduit communicates with the plunger housing portion immediately above the location of the seal sub 62. The pump control lines in this instance communicate externally alongside the plunger housing portion and the motor housing portion to the motor located at the bottom end of the motor housing portion.

In the alternative configuration of FIG. 3, the motor may instead be provided at a location above the plunger housing portion. In this instance the pump control lines communicate directly to the top end of the motor housing portion locating the motor therein so that pump control lines are not required to extend externally alongside either the motor housing portion or the plunger housing portion. The auxiliary conduit 26 in this instance however communicates between a top end of the conduit above the motor housing portion in direct connection to the production passage of the production conduit of the coiled tubing member 14 and a bottom end communicating through the wall of the plunger housing portion immediately below the seal sub 62 at the top end of the plunger housing portion.

Turning now to the embodiment of FIG. 4, in this instance the motor housing portion 22 supporting the drive linkage therein remain substantially the same as in previous embodiments, however, the plunger housing portion 24 in this instance is provided with a reciprocating pump of the type which does not include a dynamic or movable check valve 74 supported on the plunger 50 for movement therewith. In this instance the plunger 50 spans across the full cross-sectional area of the pumping chamber within the interior of the plunger housing portion with seals about the circumference thereof for sealing engagement with the interior walls of the plunger housing portion. The production passage of the plunger housing portion in this instance thus comprises merely the upper portion of the plunger housing portion 24 above the plunger 50. The auxiliary conduit 26 in this instance communicates from the end sub 28 at the bottom end of the tubing string to the top end of the plunger housing portion 24 above the motor housing portion 22. The check valve 88 is supported in series within the production passage of the auxiliary conduit 26 at the top end of the auxiliary conduit. The check valve 88 is configured to only allow upward flow from the end sub 28 at the bottom end of the auxiliary conduit to the top end of the plunger housing portion 24 at the top end of the auxiliary conduit. The stationary check valve 78 in this instance is mounted in proximity to the top end of the plunger housing portion 24 in communication between the production passage of the plunger housing portion and the production passage within the production tubing 16 of the multi-conduit coiled tubing member 14 thereabove. As the plunger 50 is stroked downwardly, the expanding pumping chamber or production passage above the plunger fills with fluid by the opening of the check valve 88 in the auxiliary conduit 26 while the stationary check valve 78 remains closed. As the plunger 50 is stroked upwardly, the check valve 88 in the auxiliary conduit 26 remains closed so that fluid is forced by the plunger upwardly through the production passage of the production tubing 16 due to the fluid pressure opening the stationary check valve 78. The hollow interior of the plunger housing portion 24 between the plunger 50 thereabove and the drive linkage therebelow receives fluid therein which communicates with a flushing passage 100. The top end of the flushing passage 100 communicates with the interior of the plunger housing portion below the plunger 50 while the bottom end of the flushing passage 100 is directed across the screen at the bottom end of the end sub 28 which locates the production intake ports 30 therein. As the plunger 50 reciprocates, fluid is drawn into and out of the flushing passage to produce a flushing action across the production intake ports 30.

In yet further embodiments, the motor 36 may comprise an electric submersible motor mounted in a similar location within the motor housing portion as either of the first and second embodiments described above. The electric motor differs in that the pump control lines in this instance comprise electrical lines in a circuit communicating between a power source at the wellhead and the motor at the bottom end of the production tubing string. The drive linkage however would remain substantially identical in configuration.

In yet further embodiments, the lead screw may take the form of a double screw to allow the sleeve and followers to reverse the reciprocating pump at the end of each stroke while the lead screw remains unidirectional. This eliminates the need for stop and start reversing by hydraulic switching at the wellhead and improves efficiency of hydraulic power delivery to drive the lead screw.

Since various modifications can be made in my invention as herein above described, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense. 

1. A motor and pump assembly for use in a wellbore with a production tubing string having a production passage therein and at least one pump control line alongside the production tubing string, the pump assembly comprising: a motor housing portion comprising: a hollow tubular housing arranged to be supported at a bottom end of the production tubing string; a motor supported within the hollow tubular housing for connection to said at least one pump control line for driving rotation of a rotary output of the motor; a drive linkage supported within the hollow tubular housing having a rotary input in connection with the rotary output of the motor and a reciprocating output which is arranged for longitudinal sliding movement relative to the hollow tubular housing responsive to rotation of the rotary input; and an auxiliary conduit extending externally alongside the hollow tubular housing and having a production passage therein for connection in series with the production passage of the production tubing string; a plunger housing portion comprising: a hollow tubular housing arranged to be supported at the bottom end of the production tubing string in series with the hollow tubular housing portion of the motor housing portion, the hollow tubular housing portion of the plunger housing portion having a production passage therein for connection in series with the production passages of the auxiliary conduit and the production tubing string; a stationary check valve supported at a stationary location within the hollow tubular housing of the plunger housing portion to span across the production passage therein so as to be operable to only allow an upward flow of production fluid therethrough; a plunger supported within the production passage of the plunger housing portion so as to be longitudinally slidable relative to stationary check valve; a movable check valve supported on the plunger for longitudinal sliding movement together with the plunger relative to the plunger housing portion, the movable check valve being operable to only allow an upward flow of production fluid therethrough.
 2. The assembly according to claim 1 wherein the drive linkage comprises: a lead screw which is rotatable with the rotary input at a stationary position in the longitudinal direction relative to the motor housing portion; a sleeve member supported within the hollow tubular housing of the motor housing portion for longitudinal sliding movement, the sleeve member having a hollow interior extending longitudinally between an open end receiving the lead screw therein and a closed end coupled to the plunger; and a follower supported on an inner side of the sleeve member in operative connection to the lead screw to drive longitudinal sliding movement of the sleeve member responsive to rotation of the lead screw.
 3. The assembly according to claim 2 wherein the follower comprising a plurality of planetary screws rotatably supported on the sleeve member at circumferentially spaced apart locations about the lead screw.
 4. The assembly according to claim 2 further comprising an annular sealing member in operative connection between the sleeve member and the housing tubular housing of the motor housing portion so as to isolate the lead screw from the production passage of the plunger housing portion.
 5. The assembly according to claim 4 further comprising hydraulic oil contained in a closed chamber surrounding the lead screw.
 6. The assembly according to claim 1 further comprising an end sub supported at a bottom end of the production tubing string and having a plurality of inlet openings at a bottom end of the end sub such that the production passages of the plunger housing portion and the auxiliary conduit are connected in series between the production passage of the production tubing string thereabove and the inlet openings of the end sub therebelow.
 7. The assembly according to claim 1 wherein the motor housing portion is supported below the plunger housing portion.
 8. The assembly according to claim 7 wherein said at least one pump control line extends externally alongside the plunger housing portion.
 9. The assembly according to claim 1 wherein the motor housing portion is supported above the plunger housing portion and wherein the production passage of the auxiliary conduit communicates in series between the production passage of the plunger housing portion therebelow and the production passage of the tubing string thereabove.
 10. The assembly according to claim 1 wherein the motor comprises a hydraulic motor and said at least one pump control line comprises a first hydraulic line and a second hydraulic line connected in a loop between the motor and a hydraulic supply at a wellhead of the wellbore for driving the motor.
 11. The assembly according to claim 10 further comprising a hydraulic switching motor arranged to periodically reverse flow in the first and second hydraulic lines so as to periodically reverse rotation of the rotary input and corresponding longitudinal movement of the reciprocating output of the drive linkage.
 12. The assembly according to claim 1 wherein the motor comprises an electric submersible motor and said at least one pump control line comprises an electric circuit in communication between the electric submersible motor and a power source at a wellhead of the wellbore for driving the motor.
 13. A drive assembly for use in a wellbore with a production tubing string supporting a reciprocating pump assembly at a bottom end thereof, and including at least one pump control line alongside the production tubing string, the drive assembly comprising: a hollow tubular housing arranged to be supported at a bottom end of the production tubing string in series with the reciprocating pump assembly; a motor supported within the hollow tubular housing for connection to said at least one pump control line for driving rotation of a rotary output of the motor; and a drive linkage supported within the hollow tubular housing having a rotary input in connection with the rotary output of the motor and a reciprocating output which is arranged for connection to the reciprocating pump assembly; the drive linkage comprising: a lead screw which is rotatable with the rotary input at a stationary position in the longitudinal direction relative to the motor housing portion; a sleeve member supported within the hollow tubular housing for longitudinal sliding movement, the sleeve member having a hollow interior extending longitudinally between an open end receiving the lead screw therein and a closed end including a coupling for connection to the reciprocating motor; and a follower supported on an inner side of the sleeve member in operative connection to the lead screw to drive longitudinal sliding movement of the sleeve member responsive to rotation of the lead screw.
 14. The drive assembly according to claim 13 wherein the follower comprising a plurality of planetary screws rotatably supported on the sleeve member at circumferentially spaced apart locations about the lead screw.
 15. The drive assembly according to claim 13 further comprising an annular sealing member in operative connection between the sleeve member and the housing tubular housing so as to isolate the lead screw from production fluids within a production passage of the reciprocating pump assembly.
 16. The drive assembly according to claim 15 further comprising hydraulic oil contained in a closed chamber surrounding the lead screw. 